A rotary member, such as a runner used in a turbine or a pump may suffer surface abrasion caused by some fluids used during operation. When a clean liquid, that is, a liquid containing few particulates is used, surface abrasion of a runner is not a significant problem except for surface abrasion caused by cavitation. However, for a runner of a hydraulic machine such as a turbine or a pump which handles water containing a large amount of sand and soil, a surface of the runner is washed out by fine particles of the sand and soil in the water, and suffers abrasion at an early stage.
A runner that is used in a hydraulic machine such as a turbine used in a power plant built in a river containing a large amount of sand and soil, especially quartz components, suffers extreme abrasion, and becomes unusable at an early stage. Thus, a rotary member such as a runner used under such an environment has been surface treated with an abrasion resistant material, but a conventional method cannot provide sufficient abrasion resistance.
Depending on types of turbines or pumps to be used, some runners have vanes of a complex shape, and surface treatment by depositing an abrasion resistant material is sometimes extremely difficult depending on spots to be treated. For example, a Francis turbine runner has a complexly curved vane, and the vane is placed between two members, that is, a main plate (a hub or a crown) and a side plate (a shroud or a band), thus surface treatment of an inside of the runner is extremely difficult.
On the other hand, various methods for surface treatment by depositing an abrasion resistant material on a surface have been known. For example, the methods include a gas powder method, an arc spraying method, a gas plasma method, a high speed flame spraying method, a spraying and melting method, or the like. The inventor studied whether these methods can be applied to abrasion resistant surface treatment of a runner, and found that sprayable materials are limited by differences in heat sources, or the like. This causes differences in abrasion resistance of treated surfaces, and further limits locations where the surface treatment can be performed depending on spraying methods.